1. Field of the Invention
This invention relates to an apparatus and method capable of testing a transducer and, in one aspect, an apparatus and method capable of determining an amount of error in an outputted signal from a displacement transducer.
2. Description of the Related Art
Generally, a displacement transducer senses a change in a position of a body or a point with respect to a reference point. Linear displacement transducers sense a change in a position of a body or point along a line or axis with respect to a reference point. While different varieties of linear displacement transducers use various techniques to sense a change in position, most have a movable, extendable portion that contacts or is attached to the body to be measured. The extendable portion can be a rod that extends from a transducer body, such as in a linear variable differential transformer (LVDT) or a magnetostrictive displacement transducer. The extendable portion can also be a wire or a cable, such as in a draw-wire transducer with displacements ranging from 0 to 25 meters or more. As the measured body or point changes position, the extendable portion of the transducer changes position, and the transducer outputs a signal corresponding to the degree of change in position. For example, if a displacement transducer has a range of 2500 mm and a designed voltage output of 0-10 volts over its range, a displacement of 250 mm should result in a voltage output of one volt. It follows that a displacement of 500 mm should result in a voltage output of two volts, and so forth.
It is advantageous if the output signal, with respect to the displacement, can be described by a curve. It is even more advantageous if the output signal, with respect to the displacement, has a linear relationship. That is, for a constant change in displacement, there is a constant change in the signal outputted from the transducer. While this is a desirable condition, some degree of error exists. For example, for a displacement of 100 mm, the corresponding signal output might be 1.012 volts; for a displacement of 200 mm, the corresponding signal output might be 2.037 volts. Thus, the outputs of transducers have associated tolerances. For example, a transducer having a displacement range of 1000 mm and a displacement tolerance of +/xe2x88x920.1% of full scale is capable of determining a displacement within 1.0 mm. That is, in this example, the transducer does not have the ability to discern changes in displacement that are less than 1.0 mm.
Accordingly, it is important that a displacement transducer is capable of operating within the tolerances specified for it. Using a displacement transducer that is incapable of operating within the tolerances specified for it in an application which requires such tolerances can bring on undesirable results.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In one aspect of the present invention, an apparatus is provided that is capable of testing a displacement transducer having an extendable portion. The apparatus includes a slide that is capable of being moved along an axis. The extendable portion of the displacement transducer is connectible to the slide so that, when the extendable portion is connected to the slide and the slide is moved, the extendable portion is extended and retracted along a path. In applications wherein the extendable portion of the transducer is longer than the slide, a displacement transducer of any length can be measured by clamping and unclamping the extendable portion and the reciprocating the slide. The apparatus also includes measuring means for determining a displacement of the slide along the axis.
In another aspect of the present invention, a method capable of testing a displacement transducer is provided including determining a plurality of electrical signal values outputted from the transducer corresponding to a plurality of displacements of the transducer and creating a statistical model based upon the plurality of electrical signal values and the plurality of the displacements of the displacement transducer. Further, the method includes determining a displacement error of the displacement transducer for each of the plurality of electrical signal values and the plurality of displacements of displacement transducer based upon the statistical model. Each of the displacement errors is examined to determine which exceed a predetermined tolerance.